The invention relates to a method for exhausting from a limited zone and an exhaust fan apparatus for the exercise of the method.
Methods so far known for the exhaustion of places of work are based on an exhaustion of the room air by means of an exhaustion device placed in a farther or lesser distance from the place of work. Such an exhaustion device is not very expedient as it first of all must have comparatively great suction capacity in order to be effective, which great capacity causes air currents with great speed from all of the room towards the exhaustion place. This draft is very unhealthy for the personnel staying near the place being exhausted. Furthermore there will be a great loss of heat caused by this vigorous exhaustion of heated air.
In order to improve the efficiency it is known to supplement the exhaustion with injection of air, which injection is done from an area near the exhaustion and directed towards the place of exhaustion. This injection causes an entrainment effect on the room air which thereby creates the flow directed towards the exhaustion. This improves the suction effect but not the unpleasant air currents and the uncontrolled exhaustion of all of the air space in front of the exhaustion.
In order to exhaust from as limited a zone as possible it has been necessary to do the exhaustion close to the individual places of work. This is in practice quite inexpedient as it considerably reduces the freedom of action around the place of work because of the presence of the exhaustion device.
The purpose of this invention is to overcome the defects and inconveniences in the known methods. This purpose is achieved by injecting a flow of air radially outward from a circumferential region surrounding the unobstructed entrance to an exhaust duct in proportion to the exhaustion at the same time of air through the exhaust duct.
Hereby a constant exhaustion with great effect is obtained which is constant within wide limits, as the exhaustion is only taking place from a limited zone along the axis of symmetry of the exhaust duct because of the entrainment effect which has been generated by the radial flow. Hereby one avoids having to suck from all of the room. This causes the exhaustion to work with great speed even far from the exhaust duct opening. The resulting concentrated exhaustion has great effect because of the limited zone of exhaustion which can be facing as needed. Hereby the loss of heat is considerably reduced and also there will be almost no perception of draft as the major portion of air will not be exhausted but remain in the room. Furthermore, the polluted air from the work space remains inside the zone of exhaustion as it does not pass the boundary surface between the exhausted amount of air and the entrained amount of air.
A nozzle comprising a cylindrical exhaust duct surrounded at its entrance end by a pressure chamber having a circumferential aperture is especially appropriate for exercise of the method. It is simple and compact without mechanical parts and it has in practice shown to function as an effective exhaustion nozzle.